Wave-induced overturning moments, moment arms, and associated forces on monopile foundations

Accurate prediction of wave-induced overturning moments is important for the safe and economical design of monopile foundations for offshore wind turbines. In this study, harmonic-specific moment arms are derived from depth integrals of the inertia force contribution up to the still-water level, yielding closed-form expressions for the effective moment arm associated with each force harmonic. These expressions are assessed against OpenFOAM simulations in an inertia-dominated regime. The results show that the inertia-based formulation, combined with modest harmonic-dependent corrections, reproduces the total overturning moment with high accuracy. Although the present validation uses simulated force harmonics, the same framework can be combined directly with higher-order Stokes-type force models for engineering applications. • OpenFOAM simulations of wave groups on a monopile quantify force and overturning moment. • Harmonic moments scale linearly with force via constant effective moment arms derived from the Morison inertia term. • In the inertia-dominated regime considered, moment arms are primarily controlled by kh and show weak sensitivity to wave steepness. • Empirical corrections to moment arms are proposed for nonlinear harmonics based on depth effects.